A secondary battery having high energy density is needed due to the rapid expansion of the market of notebook computers, mobile phones, electric cars and the like. As a method for obtaining a secondary battery having high energy density, there has been known a method of using a high capacity negative electrode material, a method of using a non-aqueous electrolyte liquid having good stability, or the like.
Patent document 1 discloses using a silicon oxide or a silicate as a negative electrode active substance for a secondary battery. Patent document 2 discloses a negative electrode for a secondary battery provided with an active substance layer comprising a carbon material particle that can absorb and desorb lithium ions, a metal particle that can be alloyed with lithium and an oxide particle that can absorb and desorb lithium ions. Patent document 3 discloses a negative electrode material for a secondary battery which is formed by coating the surface of particle, which has a structure in which a silicon fine crystal is dispersed in a silicon compound, with carbon.
Patent document 4 discloses a non-aqueous electrolyte liquid comprising a fluorine-containing phosphate ester having the structure represented below.

[In the above formula, Rf1, Rf2 and Rf3 may be the same or different, and all of these are fluorine-containing alkyl groups having 1-3 carbon atoms.]
Patent Document 5 discloses a non-aqueous electrolyte liquid comprising a phosphate ester and a bisphosphonate ester and/or a phosphonate ester.